The present invention relates to a low temperature curable coatings, more particularly to addition curable organopolysiloxane coatings that cure rapidly at low temperature.
Addition curable release coating compositions and their use as release coatings are known, see, for example, coassigned U.S. Pat. No. 4,448,815. A layer of such coating is typically applied to a substrate, such as paper, from a reactive coating bath which contains an alkenyl-functional organopolysiloxane, a hydride-functional organopolysiloxane, a precious metal catalyst and a cure inhibitor. Once applied, the layer of coating is cured by exposing the coated substrate to elevated temperature.
The cure inhibitor retards cure of the coating and enables a balance between a long useful coating bath life at low temperature and rapid cure speed at elevated temperature to be maintained. There is a constant desire in the art to provide increased cure speed without compromising bath life.
The need to subject the coated substrate to elevated temperature to cure the coating layer introduces some drawbacks to the use of addition cure organopolysiloxane release coatings coating process, in the form of energy costs, a need to rehydrate coated paper substrates after curing and a limited ability to use such coatings to coat temperature sensitive substrates, such as, for example, some polymer films. Due to these drawbacks, there is a desire in the art to provide coatings that are curable at lower temperature without compromising bath life.
In a first aspect, the present invention is directed to a method of making a coated substrate.
In a first embodiment, a method of making a coated substrate comprises: applying a layer of a coating composition, said coating composition comprising an alkenyl functional organopolysiloxane and a hydride functional organopolysiloxane, to a substrate, said substrate comprising a catalytically effective amount of a precious metal catalyst, and allowing the layer to cure.
In a second embodiment, a method of making a coated substrate comprises: applying a layer of a first component of a coating composition, said first component comprising an alkenyl functional organopolysiloxane and a catalytically effective amount of a precious metal catalyst to a substrate, applying a layer a second component of a coating composition, said second component comprising a hydride functional organopolysiloxane, to the substrate, and allowing the layers of coating composition to cure.
In a third embodiment, a method of making a coated substrate comprises: applying a layer of a coating composition, said coating composition comprising organopolysiloxane having both alkenyl and hydride radicals present on the same molecule, to the substrate, said substrate comprising a catalytically effective amount of a precious metal catalyst, and allowing the layer to cure.
The method of the present invention allows the use of a non-catalyzed coating bath having a very long useful life, while providing a highly reactive coating layer that may be rapidly cured at low temperature and thereby avoids some of the drawbacks, for example, high energy costs, the need to rehydrate paper substrates and the limited applicability to temperature sensitive substrates, that characterize typical addition cure coatings.
Another aspect of the present invention is directed to a catalyzed article comprising a substrate selected from paper sheets, polymer films, polymer coated paper sheets and metal foils, and a precious metal catalyst disposed on at least one surface of the substrate.
Another aspect of the present invention is directed to a method of forming a catalyzed article, comprising: forming a dilute catalyst by dissolving a precious metal catalyst in a volatile organic or organosiloxane solvent; or by dispersing a precious metal catalyst in a binder composition; or by dispersing a precious metal catalyst in a film forming polymer composition, and applying the dilute catalyst to the substrate, wherein the composition of the dilute catalyst and application rate of dilute catalyst on the substrate are selected to provide a selected amount of precious metal per unit area of substrate surface.